The basic method for production of carbon black has been known for some time. Generally, carbon black is produced by injecting a hydrocarbon raw material (hereinafter called "feedstock hydrocarbon") into a flow of hot oxygen-containing gas wherein the feedstock hydrocarbon is partially pyrolyzed before being quenched by a water spray. The hot gas is produced by burning a fuel in a combustion chamber. The combustion chamber is interconnected axially with a cylindrical reaction chamber and the hot gas produced in the combustion chamber flows through the reaction chamber, where the feedstock hydrocarbon is introduced into the flow of hot gas.
The feedstock hydrocarbon may be introduced into the flow of hot gas from an axial locus within the reaction chamber, or through the wall of the reaction chamber. It is often preferred to introduce the feedstock hydrocarbon through the wall of the reaction chamber because the axial injection apparatus interferes with the flow of the hot gas from the combustion chamber. As the flow of hot gas carries the feedstock hydrocarbon, the feedstock hydrocarbon is pyrolyzed to form carbon black and gaseous by-products. The pyrolysis reaction is then quenched by a spray of water. Finally, the carbon black is separated from the gas flow.
The physical properties of carbon black may be varied by controlling the process parameters of the carbon black reactor. For example, "tint" is an important property of carbon black. The particle size distribution of the carbon black affects the tint. A narrow particle size distribution gives a high-tint carbon black which imparts improved skid and traction qualities to rubber. The temperature and amount of the hot gas from the combustion chamber, the amount and distribution of feedstock hydrocarbon in the flow of hot gas, the flow pattern of hot gas and feedstock hydrocarbon through the reactor, the residence time of the feedstock hydrocarbon in the carbon black reactor, the flame length of the pyrolyzing reaction, and the amounts of impurities are parameters that affect the particle size distribution of the carbon black. These process parameters must be controlled in order to control the particle size distribution of the carbon black product.
Prior art carbon black reactors generally have cylindical reaction chambers. The temperature and amount of the hot gas from the combustion chamber can be controlled by the amount and type of fuel and the amount of air used for combustion. The amount of feedstock hydrocarbon entering the flow of hot gas can be controlled by a simple valve mechanism, but the remaining parameters of the carbon black process can be difficult to control with the cylindical reactor. One way to attempt to control the residence time of the pyrolyzing feedstock hydrocarbon in the reactor is to move the point of introduction of the feedstock hydrocarbon along the longitudinal axis of the reaction chamber. The closer the point of introduction of the feedstock hydrocarbon to the combustion chamber, the longer the residence time of the feedstock hydrocarbon.
When the feedstock hydrocarbon is introduced through the walls of the reaction chamber, the residence time is difficult to control. Moreover, as the feedstock hydrocarbon is introduced through the walls of a cylindrical reaction chamber, the feedstock hydrocarbon tends to impinge on the inner surface of the cylindrical reaction chamber around the point of introduction of the feedstock hydrocarbon. The temperature of the hot gas within the reaction chamber and thus the temperature of the curved inner surface of the reaction chamber range from 2000.degree. Fahrenheit to 3500.degree. Fahrenheit. The temperature of the feedstock hydrocarbon at the point of introduction is generally 350.degree. Fahrenheit. If the feedstock hydrocarbon is preheated to a much higher temperature it is turned into coke. Because of this extreme difference in temperatures, the impingement of the feedstock hydrocarbon on the inner surface of the reaction chamber causes thermal shock to the reaction chamber. The thermal shock erodes the inner surface of the reaction chamber and widens the cross sectional area of the reaction chamber. The eroded portion of the inner surface of the reaction chamber produces an impurity in the carbon black product called refractory grit. Another detrimental effect of the impingement of the feedstock hydrocarbon on the inner surface of the reaction chamber is an impurity called impingement coke, which is a result of the feedstock hydrocarbon contacting the high-temperature surface of the reactor. Impingement coke is a hard carbon substance with a particle size much larger than high tint carbon black.
Because of the widened cross section of the reaction chamber due to erosion, the volume of the reaction chamber becomes increased and consequently the residence time of the flow of hot gas and pyrolyzing feedstock hydrocarbon becomes increased as the reactor operates. This increased residence time provides for more reaction time and thus alters the particle size distribution of the carbon black product. The longer the residence time of the feedstock hydrocarbon, the larger the average particle size of the product. The presence of refractory grit and impingement coke in the carbon black product also affects the particle size distribution and overall quality of the carbon black. The quality and particle size control thus degrades with time as the conventional cylindrical reactor operates.
Another problem with the cylindrical prior art carbon black reactors is the inability of the feedstock hydrocarbon sprays to cover the cross sectional area of the hot gas flow when the feedstock hydrocarbon is introduced through the walls of the reaction chamber. When the feedstock hydrocarbon is sprayed into the reaction chamber through the walls of the reaction chamber, a non-circular spray pattern is formed. The cross section of the cylindrical reactors is circular and, therefore, the cross section of the hot gas flow through the cylindrical reaction chamber is also circular. Because the non-circular pattern formed by the feedstock hydrocarbon sprays does not match the circular cross section of the hot gas flow, portions (hereinafter called void hot gas) of the hot gas flow remain void of feedstock hydrocarbon spray even after the feedstock hydrocarbon has been introduced. The presence of void hot gas has detrimental effects on the carbon black process. First, the void hot gas increases the flame length of the pyrolyzing feedstock hydrocarbon. The flame of the pyrolyzing feedstock hydrocarbon begins with the injection of the feedstock and ends when the oxygen in the hot gas flow is consumed. The oxygen remaining in the void hot gas is not consumed until the oxygen contacts the feedstock hydrocarbon. This often does not occur until the void hot gas is further down stream, thus elongating the flame of the pyrolyzing feedstock hydrocarbon. The void hot gas over-pyrolyzes some of the feedstock hydrocarbon, thereby broadening the particle size distribution of the carbon black product. Moreover, some of the void hot gas escapes without ever contacting the feedstock hydrocarbon and is wasted.
Therefore, there is a need for a carbon black reactor which provides greater control over the parameters of the carbon black reaction process and consistently produces a carbon black with a narrow particle size range.